Aerosolization is a desirable means for the delivery of therapeutic or diagnostic agents. Aerosol delivery avoids the problems associated with other delivery methods such as oral administration or injection. Injections are painful, present a risk of infection to the health-care provider from an inadvertent needle-stick, and create hazardous waste from the needle and syringe. Additionally, repeated injections can result in scarring. Oral administration must overcome several obstacles to the delivery of agents, including the acidic environment of the stomach, the ability of the agent to pass through the of the intestinal wall, and first-pass metabolism of the agent by the liver. Aerosol delivery, on the other hand, allows the direct delivery of agents to areas such as the nasal tract, the respiratory tract, or the eye, as well as systemic delivery into the circulation by administration to the respiratory tract and uptake into the circulation.
Currently available methods of generating and delivering aerosols to the nasal and respiratory tract include metered-dose inhalers, dry powder inhalers and nebulizers. Available methods of delivering agents to the eye include ointments and eye drops.
Co-owned U.S. Pat. Nos. 5,544,646; 5,718,222; 5,660,166; 5,823,178; 5,709,202; and 5,906,202 describe devices and methods useful in the generation of aerosols suitable for drug delivery. A drug formulation is forcibly applied to one side of a pore-containing membrane so as to produce an aerosol on the exit side of the membrane. Aerosols containing particles with a more uniform size distribution can be generated using such devices and methods, and can be delivered to particular locations within the respiratory tract.
However, the high pressures which must be used to generate acceptable aerosols present significant limitations on aerosolization devices. Sufficient power must be provided by the devices to generate the desired pressure. Larger power sources increase the weight of these devices, and thereby decrease the mobility of patients. In portable devices, battery life is also decreased by higher power needs. Additionally, higher pressures increase the required pressure tolerances of other system components. Elevated pressures may also lead to variability in aerosol quality.